1. FIELD OF THE INVENTION
The present invention relates to a method for hot embossing a conductor track onto a substrate.
2. DESCRIPTION OF RELATED ART
The hot embossing of conductor tracks on substrates, which are made of a polymer material in particular, represents an environmentally friendly possibility for manufacturing conductor tracks. In known hot embossing methods, first the substrate having the desired microstructure is manufactured, for example, using an injection-molding method. The substrate is then placed, together with a metal film situated thereon, in a press, after which the conductor tracks are embossed as depressed structures under application of pressure and temperature using a structured embossing die. The residual film on a raised structure plane of the substrate is drawn off of the substrate again after the embossing process. The drawing-off process is extremely critical. The success of the drawing-off process is essentially a function of the tear resistance of the metal film. Film residues which are not drawn off may result in short circuits between the conductor tracks. During the drawing-off process, the actual recessed conductor tracks, which are spaced apart from the raised structure plane, may also be drawn off or damaged, in particular if the embossing pressure was not sufficiently great. On the one hand, during the drawing-off process, the (raised) residual film to be drawn off may thus not be pressed too strongly onto the substrate, which has the result that the recessed, lower-lying conductor tracks are only applied using this maximal force. On the other hand, the embossing force must be selected as sufficiently great to ensure that the conductor tracks adhere sufficiently strongly to the substrate after the drawing-off process of the residual film.
Furthermore, the known method has the disadvantage that the conductor tracks may exclusively be introduced in a recessed structure plane. This has the result that the fixing of semiconductor chips on the conductor tracks is only possible using an adhesive flip chip method if the height difference between the conductor tracks and the raised structure plane is less than the height of the bumps. For gold stud bumps, this height is approximately 50 μm. This is difficult to achieve technologically, because with embossing depths this low, practically no punching of the metal film is possible due to a minimum thickness of the metal film used, and therefore no conductor tracks may remain standing on the substrate. Known substrates having embossed conductor tracks are also only usable in a limited way for a solder flip chip process, because the solder bumps are spherical and would thus only be acceptable for narrow conductor tracks of low embossing depths.